The purpose of this investigation is to study the regulation of intracellular protein degradation in E. coli. Experiments previously undertaken in this laboratory using 3H leucine labeling have indicated that E. coli stringent cells degrade protein more rapidly than isogenic relaxed cells under conditions of metabolic stress, particularly carbon or nitrogen starvation. Therefore, these conditions were selected for studies directed toward the isolation of one or more enzyme systems which exhibited a sharp reduction in intracellular level following provocation of the stringent response, as well as characterization of the cellular components responsible for this effect. Using 32P as a probe to monitor changes in phospho-proteins an increase in low molecular weight labeled proteins was observed in extracts following a stringent response. Similar results were obtained by incubating 14C-(AMP)-glutamine synthetase with cold extracts prepared in the same manner. Experiments have been designed to study these effects further. Techniques utilized in these studies have included polyacrylamide pore gradient electrophoresis, isotopic labeling, column chromatography, autoradiography, and enzymatic assay of functional proteins.